1. Field of the Invention
This invention relates to a fuel control system for an internal combustion engine utilized in an automobile or the like, and particularly to means for determining malfunctions such as deterioration or damage etc. of various sensors utilized in this system.
2. Discussion of Background
The fuel control system for an internal combustion engine is disclosed, for instance, in Japanese Examined Patent Publication No. 56340/1987, or Japanese Unexamined Patent Publication No. 11383/1987. It is an effective means for the promotion of running performance and efficiency of an engine, as well as exhaust gas purification. In the above fuel control system for an internal combustion engine, as shown in the above patent publications, various sensors such as an air-flow sensor, an oxygen sensor, a revolution sensor, and a boost pressure sensor, and actuators are utilized. When these sensors or actuators are out of order, the performance of the fuel control system is lowered. However, even when these sensors or actuators are out of order, they are still used as they are so far as the lowering of the system function does not cause major problems in the running of an automobile. In such cases, it has recently been realized that, especially when the exhaust gas purification function is lowered, the system considerably and adversely impacts the environment. Therefore, it has formerly been proposed that a complete malfunction of sensors and actuators should be detected by the snapping of a wire or a short circuit.
It has formerly been possible to detect and inform the complete malfunction of sensors and actuators by snapping of a wire or a short circuit, in the fuel control system for an internal combustion engine. However, it has not been possible to detect the deterioration or the damage of functions not as severe as a complete malfunction. Especially, in case of analogue type sensors, it is difficult to detect the lowering of functions. In order to carry out the detection, the only method is to provide the same or the same kind of sensors in plural numbers, which becomes considerably disadvantageous economically.